1. Field of the Invention
The present invention relates to an electron vacuum image intensifier for use in an x-ray diagnostic installation, and in particular to improvements in the carrier plate structure for such an intensifier.
2. Description of the Prior Art
Various types of x-ray diagnostic installations are known in the art having different configurations, however a basic list of components for such systems generally includes a means for generating an x-ray beam, an x-ray image intensifier disposed after the subject through which the x-ray beam has passed for converting the image at an input screen into an electron image, a means for electronically and optically accelerating the image components onto an output luminescent screen, where the image is generated at the inside wall of the output window of a vacuum bulb in the intensifier. The intensifier includes a carrier having a thickness dimensioned such that total reflections occurring at the image exit surface of the intensifier output window at most return back to regions of the luminescent screen which are outisde of the observation region. Such an apparatus is described, for example, in U.S. Pat. No. 3,622,786.
In conventional x-ray diagnostic installations of this type having an image intensifier followed by an objective lens system, which is generally an objective system of a television chain, a problem exists in combining the separately constructed devices comprising the installation, that is, combining the image intensifier and the separate objective system. Distances between the surfaces through which the output image is transmitted remain in the optical transmission path, resulting in reflections at the optical boundary surfaces, in particular, at the carrier of the output luminescent screen of the image intensifier. Such images as well as the associated light scatter resulting therefrom deteriorate the image contrast, and additionally increase the background of the image thereby significantly reducing the image quality.
For avoiding the existance of boundary surfaces, optical fiber connections have been used in x-ray television chains, for example, as disclosed in U.S. Pat. No. 3,058,021. The fiber connections generally extend between the output of the image intensifier and the input of a following television camera. The use of such optical fibers, however, has the disadvantage that resolution losses also occur in addition to the light loss due to light absorption of the optical fibers. Moreover, division of the incoming light into a plurality of different receivers is not possible with the use of optical fibers. Attempts have been made to eliminate such unwanted background by improving the absorption and contrast of the transmissive material. For this purpose gray glass has been employed for use as the material comprising the luminescent screen carrier, or as an absorption layer, however the use of such glass has not been successful because such glass exhibits still a significant light loss and has the further advantage of being costly to manufacture.
Another effort to improve the output image of a picture tube is disclosed in European laid-open patent application No. 00 87 674 wherein the glass carrier of the output luminescent screen is made so much thicker that total reflections at the inside of its output surface do not proceed to the observation surface. In order to employ a luminescent screen of this type with a standard carrier, the output surface of the screen is bonded to the inside surface of the output window pane of the tube bulb to form a stack having a suitable thickness. In order to achieve adequate thickness, a transparent plate is additionally glued to the outside of the window pane under certain conditions. Therefore production of such a stack requires at least one glueing operation inside of the tube bulb. Acceptable adhesives are not currently available which are optically fault-free and vacuum-resistant, therefore picture tubes constructed in accordance with the aforementioned European application have not been commercially manufactured.